The objective of this proposal is the investigation of the effects of the interaction between marihuana, the most frequently abused illicit drug, and the frequently abused CNS stimulants, cocaine and amphetamine, with ethanol. The proposed studies will follow a double-blind, placebo-controlled, digram-balanced, latin square design. Because of the relevance of public health and public safety, the main focus of investigation will be on the effects of the drug/ethanol interactions on the performance of skills necessary to drive an automobile or to operate machinery with precision. In addition, the effects of drug interaction on relevant neuropsychologic, cardiovascular, and endocrine parameters, and on possible changes in drug absorption and disposition will be investigated. The proposed investigations will have the following characteristics: 1) An adequate number of subjects will be tested in each of the studies. The proper size of the sample has been based on power calculations. 2) Two doses of the companion drug and an effective dose of ethanol will be investigated. 3) The time of administration of the companion drug with respect to the time of administration of ethanol will be studied. 4) Plasma concentrations of ethanol and the companion drugs will be determined. 5) The design of the studies will permit a comparison of the effect of each drug alone and in combination with ethanol.